Bacteriology & Parasitology
Samuel, J Bacteriol Parasitol 2016, 7:1
http://dx.doi.org/10.4172/2155-9597.1000261
Review Article
Open Access
Opportunistic Parasitism: Parasitic Association with the Host that has
Compromised Immune System
Fikresilasie Samuel
Department of Medicine, Ambo University, Ambo, Ethiopia
*Corresponding
author: Fikresilasie Samuel, Department of Medicine, Ambo University, Ambo, Ethiopia, Tel: +251929050512; E-mail: fikre16sam@gmail.com
Received date: October 05, 2015; Accepted date: February 17, 2016; Published date: February 23, 2016
Copyright: © 2016 Samuel F. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use,
distribution, and reproduction in any medium, provided the original author and source are credited.
Abstract
A symbiotic association between opportunistic parasites and immunocompromised hosts is known as
opportunistic parasitism. The abnormality of immunity is caused by different factors: Aging enhances susceptibility to
severe infections; malnutrition has significant depressing consequences for immune function; an
immunosuppressant substance alcohol can interfere with the functions of many of the cells and molecules those are
components of the immune system; infectious pathogens are also major causal agents of immunosuppression.
Combined effect of these factors makes the host to be susceptible for opportunistic parasitic infections. In this review
the promising factors which induce immune disorder and exemplary opportunistic parasitic infections which illustrate
the real sense of opportunistic parasitism are well discussed.
Keywords: Opportunistic parasite; Immunity; Host; Parasitism
Introduction
Opportunistic parasitism can be defined as a symbiotic association
between opportunistic parasites and immunocompromised hosts; so
that the parasite causes opportunistic parasitic infection (OPI). OPI
occur enthusiastically with organisms that are recognized pathogens,
but are commonly caused by commensals or other normally nonpathogenic agents when host resistances are weaken by different
environmental or natural factors [1].
OPI may not cause severe pathological changes in
immunocompetent hosts as long as the immune system is functioning
normally [2]. However when the immune system is weaken due to
particular conditions, opportunistic parasites take this advantage to
initiate an infection [3]. Many people have impaired immune systems
as a result of many factors: diseases (like HIV infection or malignant
diseases), medical procedures (such as organ transplants) [2], aging,
chemotherapy and others. For these reasons, the system acquired
different defects (humeral or cell mediated). This will establish
favorable condition for opportunistic parasites to flourish over the host
system and cause a disease [4].
Review
The normal immune system task is depending on the interaction of
enormous variety of cells and molecules. Which may involves many
different mechanisms some nonspecific (i.e., generically applicable to
many different pathogenic organisms) and others specific (i.e., their
protective effect is directed to one single organism) to protect our body
from infectious agents. Nevertheless, multiplicity of different defects as
a result of diverse factors can diminish its competence badly; these
deficiencies put in the same end- result, increased susceptibility to
infection [5,6]. This review discusses the basic concept of opportunistic
parasitism and provides better definition of this association via
explaining major factors which induce immune system impairment. As
J Bacteriol Parasitol
ISSN:2155-9597 JBP, an open access journal
well, three opportunistic parasitic infections are well discussed to
exemplify others.
Major Risk Factors and Immune System Impairment
Age and stress
Resistance to the disease tends to be weaker in childhood and old
age [7]. Aging enhances susceptibility to severe infections, which is
related with a depression of cellular immunity. It has direct
consequence on development of frequent and rigorous infection,
which further increases morbidity, dependence and fatality in elderly
population [8]. In addition to aging, the immuno-suppressive effect of
stress contributes to the immune defects that give rise to the prevalence
of infectious illnesses in older adults [9]. Studies on stress in older
adults provide evidence that increased stress exposure, poor stress
buffering, exaggerated stress reactivity, unlimited anxiety duration, and
probably diminished restorative processes have effects that mimic,
aggravate, and sometimes speed up the effects of aging on immunity
[9].
Malnutrition
Nutrition has been clearly identified as key factor for human
development, not only as a conditioning factor for health but also as
determinant of quality of life throughout the lifecycle and of overall
development. Specially, in order to function competently our immune
system needs nourishment [10]. Calorie, protein, vitamins and
minerals (such as iron, copper and zinc) intakes are very important [7].
The word ‘malnutrition’ expresses any disorder resulting from an
insufficient or unbalanced diets, or a malfunctioning to absorb or
assimilate nutritional elements. It could be protein-energy
malnutrition or micronutrient deficiencies [10]. Usually, poor protein
intake and insufficient amount of vitamins and minerals in the diet
have significant depressing consequences for immune function [11].
All these conditions are associated with significant impairments of
Volume 7 • Issue 1 • 1000261
Citation:
Samuel F (2016) Opportunistic Parasitism: Parasitic Association with the Host that has Compromised Immune System. J Bacteriol
Parasitol 7: 261. doi:10.4172/2155-9597.1000261
Page 2 of 4
cell-mediated immunity, antibody concentrations, phagocyte function,
complement system, and cytokine production [10,12].
Cryptosporidium spp are well recognized as causes of diarrheal disease
during waterborne epidemics and in immunocompromised hosts [18].
In conclusion, there is cyclical relationship between malnutrition
and immunity. Poor nourishment consequences weight loss, growth
faltering, lowered immunity and mucosal damage. These increase
vulnerability of the host to communicable diseases and lead to
immunological impairments. As a result, metabolic responses change
nutritional status of the individual through loss of appetite,
malabsorption and altered metabolism [13].
The degree of the disease is mostly dependent on the immune status
of the host, whether the infection is self-limiting or continual. It is well
known that, both branches of the immune system are required for
complete improvement of the disease [19]. The studies on the
mechanisms of immunity to cryptosporidiosis pointed out that, the
spectrum and severity of disease in immunocompromised individuals
with cryptosporidiosis reflect the importance of the T-cell response
since the most severe disease is seen in individuals with defects in the
T-cell response [20].
Alcohol
Alcohol is an immunosuppressant substance, which affects both cell
mediated and humeral immunity, as does severe malnutrition [14]. It
interferes with the functions of many of the cells and molecules those
are components of the immune system. For example, alcohol slows
down the functions of Phagocytes (i.e., neutrophils, Monocytes, and
macrophages). It also changes the production of signaling molecules
that facilitate to organize the immune response (i.e., cytokines) [15].
The dysfunction of the immune system makes the patient susceptible
to enormous collection of infectious pathogens, resulting in biomedical
consequences such as increased risk of infections after surgery,
traumatic injury, or burns; of liver disease; of opportunistic infections
in the lungs; and of accelerated development of HIV disease [14,16].
As a result, immunocompromised adults and children, especially
those with AIDS, children in day care, travelers to endemic regions,
dairy or cattle farm workers of their families or contacts, household
contacts of cases or carriers, and possibly owners of infected dogs or
cats or their neighbors are at greatest risk [21]. As well, individuals
with neoplasm, severe combined immunodeficiency syndrome and
acute leukemia (most commonly in children) are associated with
increased risk of severe cryptosporidiosis disease [20]. To conclude,
immunodeficiency increased the risk of having opportunistic parasites
and diarrhea. In the immunocompromised host, infection is
prolonged, sometimes asymptomatic, but may result in chronic
debilitating diarrhea with dehydration, malabsorption, and wasting
[22].
Infection and drug
Public health measures to reduce contamination of water supplies
and vigilant surveillance will reduce the risk to populations [23].
Besides, the widespread use of antiretroviral therapy does appear to be
having a beneficial effect on recovery from cryptosporidiosis and on
the frequency of infection in human immunodeficiency virus-positive
patients. Therefore, increasing patient immune status and screening at
least for those treatable parasites is important [24].
Infectious
pathogens
are
major
causal
agents
of
immunosuppression. Specially, acquired immunosuppression due to
pathogens is primarily caused by viruses that invade the cellular
compartment of the immune system [7]. For illustration, viral
infection of cells naturally leads to the secretion of interferon alpha
(IFNα) by that cell. It is protective for cells in the local setting. On the
contrary, IFNα inhibits the G1 phase of the cell cycle, producing a
momentary immunosuppression since cells responding to IFNα
cannot clonally enlarge. In addition to immunosuppression induced by
IFNα, the HIV itself induces immunosuppression in a number of ways,
the destruction of CD4+ T cells, cells necessary for almost every part of
immunity. Other viruses, such as measles, can too temporarily depress
T cell function [7].
Besides to infections, drugs recommended for treatment contribute
to impair the immune system. These cause immunodeficiency, either
purposely or accidentally [7]. For example, cancerous diseases are
often treated by administration of cytotoxic drugs intended to kill the
tumor cells. These drugs are not cancer cell-specific and other
proliferating cells are also destroyed. Cytotoxicity to immune cells
causes nonspecific immunosuppression. In addition, to combat the risk
of graft rejection, transplant patients are intentionally given
immunosuppressive drugs, many of which inhibit the secretion of
cytokines that enhance immune responses. These patients are thus at
risk of the same infectious disorders seen in other immune defects [5].
Exemplary Opportunistic Parasitic Infections
Cryptosporidiosis
Species of the genus Cryptosporidium are protozoan parasites
(Apicomplexa) that cause gastroenteritis in animals and humans. Of
these Cryptosporidium parvum and Cryptosporidium hominis are the
major causative agents of human cryptosporidiosis [17].
J Bacteriol Parasitol
ISSN:2155-9597 JBP, an open access journal
Toxoplasmosis
Toxoplasmosis is an opportunistic parasitic infection caused by
obligate intracellular protozoan parasite Toxoplasma gondii, a parasite
belonging to the phylum Apicomplexa. The disease is primarily
transmitted by ingesting undercooked or raw meat containing tissue
cysts, or by ingesting food or water contaminated with oocysts [6].
Toxoplasma invades any cell by an active invasion process involving
motility and molecular secretion. Its success as an invasive organism
resides on its high trans-epithelial migration capability reaching
privileged organs such as brain, eye and placenta in pregnant women.
Infection in pregnant women may lead to abortion, stillbirth or other
serious consequences in newborns [25]. Toxoplasmosis affects up to
one-third of the global human population. Sero-prevalence studies in
different communities of Ethiopia showed that the general prevalence
of the disease is about 80% in the adult population [6]. And up to 41%
in children aged 1-5 years [26].
Immunosuppression due to treatment after transplantation or
related with HIV infection raises exposure to numerous opportunistic
infections, counting toxoplasmosis. The disease central nervous system
(CNS) toxoplasmosis affects the brain and occurs almost exclusively
due to reactivation of latent infection [27]. It is very important
opportunistic infection in AIDS patients. Abnormal cytokine profile
and impaired cytotoxic T cell functionality are responsible for easy
susceptibility to this infection [28]. The lung is also a major site of
infection after the CNS toxoplasmosis in immunocompromised
peoples. AIDS patients having CD4+ T cell count <100 cells/μl of blood
Volume 7 • Issue 1 • 1000261
Citation:
Samuel F (2016) Opportunistic Parasitism: Parasitic Association with the Host that has Compromised Immune System. J Bacteriol
Parasitol 7: 261. doi:10.4172/2155-9597.1000261
Page 3 of 4
can have reactivation from asymptomatic latent infection. However,
most vulnerable patients are those having CD4+ T cell count <50 cells/
μl of blood [28].
In transplant recipients toxoplasmosis is common and clearly stated
in different studies. It occurs by reactivation of latent infection or is a
primary infection if a donor organ containing encysted T. gondii was
transplanted into a seronegative recipient [29]. In addition, studies in
Korea have announced that toxoplasmosis is a rare but can be fatal
complication in hematopoietic stem cell transplant recipients, usually
associated with allogeneic hematopoietic stem cell transplantation
(HSCT) [30].
Educating the public about the risks associated with unhealthy food
and life style habits, tracking serological examinations to special
populations and measures to strengthen food and occupational safety
are recommended to avoid toxoplasmosis [25]. Finally, ART treatment
lowers the incidence of toxoplasmosis in HIV patients [28].
factors which provoke the human immune system to be impaired. Such
as: age, infection, alcohol etc. So that opportunistic organisms use the
advantage to initiate an infection.
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Samuel F (2016) Opportunistic Parasitism: Parasitic Association with the Host that has Compromised Immune System. J Bacteriol
Parasitol 7: 261. doi:10.4172/2155-9597.1000261
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